A steam power installation is normally used for generating electrical power or for driving a machine. It involves a working medium, usually a water-water/steam mixture, which is fed through a steam-generating circuit of the steam power installation, being converted into steam in an evaporator or steam generator (boiler). The steam that is generated expands to produce work in a steam turbine and is then fed to a condenser. The working medium condensed in the condenser is then fed via a pump to the boiler again for generating steam.
In a generally known steam power plant of this type, the condensate used as feed-water is successively preheated to close to the boiling temperature by means of partial steam mass flows from the turbine steam volume, thereby increasing the thermodynamic efficiency of the whole process. By removing the steam from the turbine steam volume, however, the subsequent steam turbine stages can extract less power from the steam fluid.
A method for operating a steam power plant is known from EP-A2-1 055 801, in which the condensate used as feed-water is successively preheated to close to the boiling temperature by means of partial steam mass flows from the turbine steam volume.
In order to avoid the reduction in power extraction in the subsequent steam-turbine stages, it is provided that the heat emitted from fuel cells is used to preheat the condensate. Preheating the feed-water from the heat emitted from the fuel cells, and the associated increase in the amount involved in the expansion, achieves an increase in the steam process efficiency. The fuel-cell arrangement incorporated in the preheating line of EP-A2-1 055 801 is a relatively complex and costly way of achieving preheating by the external supply of heat via the fuel cells.